Low-Complexity Subband Digital Predistortion for Spurious Emission Suppression in Noncontiguous Spectrum Access

2018 52nd Asilomar Conference on Signals, Systems, and Computers

Abdelaziz

et al. 2018

Self Cite

In this article, we propose a novel digital predistortion (DPD) solution that allows to considerably reduce the complexity resulting from linearizing a set of power amplifiers (PAs) in single-user large-scale digital beamforming transmitters. In contrast to current state-of-the art solutions that assume a dedicated DPD per power amplifier, which is unfeasible in the context of large antenna arrays, the proposed solution only requires a single DPD in order to linearize an arbitrary number of power amplifiers. To this end, the proposed DPD predistorts the signal at the input of the digital precoder based on minimizing the nonlinear distortion of the combined signal at the intended receiver direction. This is a desirable feature, since the resulting emissions in other directions get partially diluted due to less coherent superposition. With this approach, only a single DPD is required, yielding great complexity and energy savings.Index Terms-5G, digital predistortion, power amplifiers, digital beamforming, large-array transmitters, out-of-band emissions, power amplifiers.

Section: Simplified Learning Architecturementioning

confidence: 95%

Digital Predistortion in Large-Array Digital Beamforming Transmitters

Brihuega

2018 52nd Asilomar Conference on Signals, Systems, and Computers

Abdelaziz

et al. 2018

Self Cite

“…As a result, adaptive learning algorithms will suffer from slow convergence and potentially high excess mean square error, thus limiting the cancellation performance. To ensure faster and smoother learning and high cancellation performance, as well as better numerical properties in digital hardware implementations, the basis functions can be first orthogonalized with respect to each other -an approach that is widely adopted in SI cancellation and digital pre-distortion (DPD) processing contexts in general [17], [33]. To shortly outline the orthogonalization procedure, we switch to vector-matrix notations, and collect the instantaneous delayed basis function samples in a vector as…”

Section: A Basis Function Orthogonalizationmentioning

confidence: 99%

Adaptive Nonlinear RF Cancellation for Improved Isolation in Simultaneous Transmit–Receive Systems

Kiayani

Waheed

IEEE Trans. Microwave Theory Techn.

et al. 2018

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This paper proposes an active radio frequency (RF) cancellation solution to suppress the transmitter (TX) passband leakage signal in radio transceivers supporting simultaneous transmission and reception. The proposed technique is based on creating an opposite-phase baseband equivalent replica of the TX leakage signal in the transceiver digital front-end through adaptive nonlinear filtering of the known transmit data, to facilitate highly accurate cancellation under a nonlinear power amplifier (PA). The active RF cancellation is then accomplished by employing an auxiliary transmitter chain, to generate the actual RF cancellation signal, and combining it with the received signal at the receiver (RX) low noise amplifier (LNA) input. A closed-loop parameter learning approach, based on the decorrelation learning rule, is also developed to efficiently estimate the coefficients of the nonlinear cancellation filter in the presence of a nonlinear PA with memory, finite passive isolation, and a nonlinear LNA. The performance of the proposed cancellation technique is evaluated through comprehensive RF measurements adopting commercial LTE-Advanced transceiver hardware components. The results show that the proposed technique can provide an additional suppression of up to 54 dB for the TX passband leakage signal at the LNA input, even at very high transmit power levels and with wide transmission bandwidths. Such novel cancellation solution can therefore substantially improve the TX-RX isolation, hence reducing the requirements on passive isolation and RF component linearity, as well as increasing the efficiency and flexibility of the RF spectrum use in the emerging 5G radio networks.

“…A detailed analysis of the nonlinear distortions at the IM3 and IM5 sub-band has been done in [23] when a ninth-order PA is excited with a dual carrier signal as in (1). We hereby present the distortion components up to the ninth order at the IM3+ sub-band, which read…”

Section: Sequential Learning Of Imsub-band Dpd Coefficientsmentioning

confidence: 99%

“…However, for fast and smooth learning of the proposed sub-band DPD coefficients, a basis function orthogonalization procedure was proposed earlier in [23]. In this paper, we use an orthogonalization procedure which allows us to learn the DPD coefficients with different orders sequentially instead of concurrently.…”

Section: Sequential Learning Of Imsub-band Dpd Coefficientsmentioning

confidence: 99%

See 1 more Smart Citation

Low-complexity, Multi Sub-band Digital Predistortion

Tarver

Abdelaziz

et al. 2017

J Sign Process Syst

Self Cite

The nonlinearities of power amplifiers combined with non-contiguous transmissions found in modern, frequency-agile, wireless standards create undesirable spurious emissions through the nearby spectrum of data carriers. Digital predistortion (DPD) is an effective way of combating spurious emission violations without the need for a significant power reduction in the transmitter leading to better power efficiency and network coverage. In this paper, an iterative, multi subband version of the sub-band DPD, proposed earlier by the authors, is presented. The DPD learning is iterated over intermodulation distortion (IMD) sub-bands until a satisfactory performance is achieved for each of them. A sequential DPD learning procedure is also presented to reduce the hardware complexity when higher order nonlinearities are incorporated in the DPD learning. Improvements in the convergence speed of the adaptive DPD learning are also achieved via incorporating a variable learning rate and interpolation of previously trained DPD coefficients. A WarpLab implementation of the proposed DPD is also shown with excellent suppression of the targeted spurious emissions.